Osogovo or Osogovska Planina (Осоговска планина or Осоговска Планина) is a mountain and ski resort between southwestern Bulgaria

Bulgaria

Bulgaria , officially the Republic of Bulgaria , is a parliamentary democracy within a unitary constitutional republic in Southeast Europe. The country borders Romania to the north, Serbia and Macedonia to the west, Greece and Turkey to the south, as well as the Black Sea to the east...

 (Kyustendil Province

Kyustendil Province

-Religion:Religious adherence in the province according to 2001 census:-Language:Mother tongues in the province according to 2001 census:* 153,242 Bulgarian * 7,929 Roma  * 1363 others and unspecified -Ethnic groups:...

) and northeastern Republic of Macedonia

Republic of Macedonia

Macedonia , officially the Republic of Macedonia , is a country located in the central Balkan peninsula in Southeast Europe. It is one of the successor states of the former Yugoslavia, from which it declared independence in 1991...

, (Kočani

Kocani

Kočani is a town away from Skopje, situated in the Eastern part of the Republic of Macedonia, with population of 28 330. The town of Kočani is the seat of Kočani Municipality.-Geography and population:...

 and Kriva Palanka

Kriva Palanka

Kriva Palanka is a town located in the northeastern part of the Republic of Macedonia. It has 14.558 inhabitants. The town of Kriva Palanka is the seat of Kriva Palanka Municipality which has almost 21.000 inhabitants....

 municipallities). It is about 110 km (68.35 mi) long and 50 km (31.07 mi) wide, the highest peak being Ruen (Руен) at 2251 m, which constitutes the main orthographic knot on the very border between Bulgaria and the Republic of Macedonia.